Physics Photo of the Week
January 25, 2013
Stereo Moon - by Don Collins and Tom Overman
These
images were taken from two widely separated points on Earth
at the same universal time. Tom Overman, WWC 1984
graduate, lives in Honolulu, Hawaii. Tom took the left
image on December 27, 2012 (the night of full Moon) at 10:00
pm Hawaii time. Don took the right image from
Swannanoa, NC at 3:00 am the following day. Both
events occurred at the same Universal Time (0800 UT 28
December 2012). This project fulfills an idea that Tom
had expressed several years ago to see the stereo effect of
imaging the Moon from two different points on the Earth at
simultaneous times. Aside from color, these images
look identical. The color difference is attributed to
the difference in humidity at the two sites.
One method to see the stereo 3-D effect (not
recommended) the reader may get rather
close to the above images and stare at them cross-eyed (so
the right eye is focused on the left image; left eye focused
on the right) and merge the images. It gives the
viewer a bad headache. A much more satisfying result
may be obtained by displaying the two images overlapped -
one displayed in blue the other in red called a blue/red
anaglyph. The blue/red anaglyph requires blue/red
glasses to view the 3-D effect. Click here to view the
anaglyph produced by Michael Collins. Blue/red
glasses may be obtained mail-order from Educational
Innovations (http://www.teachersource.com/category/s?keyword=red%2Fblue+glasses).
Don has placed a few pairs on reserve in the Martha Ellison
Library at Warren Wilson College.
We can see the small shift of the features on the
Moon due to the 7000 km separating Swannanoa and Honolulu by
blinking the two images (shown at right). The Honolulu
image is the blinked image in which the features are
slightly rotated to the left on the page (celestial East)
because Honolulu viewed the Moon from much further west on
the Earth (left on the images). Celestial north is the
top of the images. In other words Honolulu sees around
the west side of the Moon more than Swannanoa, similar to
seeing more of the west side of a building by moving further
west.
We measured the shift in pixels between the Swannanoa
view and the Honolulu view (6 pixels ± 1 pixel) or
1/550 to 1/750 the diameter of the Moon. Using
geometry, the separation of the two cities, and the fact
that the Moon's diameter is 1/4 the diameter of the Earth we
have determined that the distance from the Earth to the Moon
is between 42 and 57 Earth radii. This compares
favorably with with the accepted value of about 60 Earth
radii. Longer focal length telescopes will give more
precise results.
Tom had also figured out the size and distance of a
model Moon if we considered the two cities (Honolulu and
Swannanoa) as the right and left eyes of an observer whose
eyes are separated by 70 mm. The model moon would be
the size of a ping pong ball located about 3.7 meters from
the observer (across a typical residential room).
Coordinating this project between two widely-separated
observers has been lots of fun! Many thanks to all who
helped! The image of the Moon from Swannanoa was made
with a Questar 3 1/2 inch telescope donated to Warren Wilson
College by Ralph Brown of Chattanooga, TN.
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.
Click here to see the Physics Photo of the Week Archive.
